The present invention relates generally to moisture control devices and more particularly, to dual column, solid desiccant dehumidifiers and dehydrators which may or may not be used in combination with central heating/air conditioning systems. Conventional apparatus of this type normally include an air blower and a source of heat applied to the column being regenerated. Ambient air always includes an existing water load which it is sometimes desirable to minimize in order to increase the shelf life of certain products, increase the comfort level in a controlled space or to save energy when cooling is necessary.
A hair dryer having two desiccant units, connected to a blower and a damper means alternately providing communication between one of the desiccant units with a conduit to a hair dryer hood. A portion of the heated, dry air is alternately directed through the other desiccant unit to regenerate such desiccant unit. During the regeneration process, a heating element is required to heat the desiccant material to facilitate regeneration of the desiccant material, as illustrated, for example, in U.S. Pat. No. 3,304,623.
It has also been conventional to furnish dryers with a desiccant material as illustrated in U.S. Pat. Nos. 2,773,313; 2,738,592; 2,735,507; 2,563,042; and 2,376,095.
Additionally, it is known to provide a dual chambered gas dryer with a by-pass valve to regenerate an alumina desiccant material by recycling part of the air through one of the dual chambers, as illustrated in U.S. Pat. No. 3,803,724.
The prior commercial drying apparatus have several disadvantages as follows: first, the desiccant material in the desiccant units is generally densely packed, and the units have a long cycle time, i.e., from 30 minutes to several hours before alternating from the drying to regeneration cycle. This necessitates a large amount of desiccant material, increasing the unit cost. Further, the long cycle time causes the desiccant to become less and less efficient, as the desiccant approaches saturation, reducing the drying capability of the unit. The long cycle time also allows the heat of adsorption to dissipate from the desiccant material, wasting energy and necessitating the addition of heat energy to regenerate the desiccant. In addition, the heat necessary to regenerate the desiccant material may put heat into the controlled space which would increase the amount of energy required for cooling. Further, prior apparatus heated the desiccant directly by placing heaters in the desiccant material or by heating the ambient air before the existing water load was removed, both methods requiring substantial amounts of energy. Finally, the relatively large pressure drop associated with densely packed desiccant units, requires a costly high powered blower operating at high static pressure to move the air through the unit, further increasing the size and cost of the dryer.
The present invention is directed to a moisture control device which eliminates the foregoing problems encountered in removing the existing water load from ambient air.